Hi Stefan,
The helium is normally used for back side cooling of the wafer, so that
the temperature of the bottom chuck of the RIE is distributed evenly to
the wafer(as helium is a very good thermal cond.) so you see if you have
temperature distributed evenly on the wafer and the plasma starts etching
the anisotropy, selectivity is preserved at every point on the wafer.
regds
Ravi Shankar
Semiconductor Complex Ltd,
India

On Fri, 8 Mar 2002, Stefan Wiechmann wrote:

> I am also using CHF3+O2 to etch SiO2/Photoresist
> and wonder how helium helps to improve uniformity ?
>
> Stefan Wiechmann
>
> _______________________________________________
> Von: [email protected] [mailto:[email protected]]Im
> Auftrag von [email protected]
> Gesendet: Donnerstag, 7. Marz 2002 21:36
> An: [email protected]
> Betreff: Re: [mems-talk] how to etch SiO2 with RIE
>
>
> There are many choices depending on the results you are looking to obtain.
> CF4+4to8% O2 is pretty standard for oxide etching. You will probably need to
> combine that with Helium to produce uniform results. We have also used SF6 +
> Helium and it has some advantages with respect to etch rate and selectivity
> to resist. If you would like to discuss further with things like etch
> thickness desired, masking material and other details just drop me an email.
> Bob Henderson
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